Casino billionaire and prominent GOP backer Sheldon Adelson engaged in “legal sadism” against a Jewish political group critical of him, the organization charges.

The National Jewish Democratic Council is “in tatters, barely functioning,” after spending five years fighting — and ultimately defeating — a defamation claim brought against it by Adelson, the group claims in a Manhattan Federal Court lawsuit.

Adelson, worth an estimated $35 billion, claimed the Washington D.C.-based NJDC defamed him when it linked online to an Associated Press article about a former Adelson employee who had accused the billionaire of personally approving prostitution at one of his resort properties.

A court eventually tossed Adelson’s claim. But NJDC never recovered, lawyer Richard Emery said.

“Because of the lawsuit, nobody would contribute anymore. There were lots of people who shunned NJDC,” he said. “He destroyed it.”

NJDC is seeking unspecified damages. Adelson’s lawyers did not return a message.